The patello-femoral joint of the knee is an articulation between the patella and femur. The joint consists of an articular surface on the posterior of the patella and a corresponding articular surface on the anterior of the head of the femur which is termed the trochlea. The posterior of the patella is contoured as a ridge, while the trochlea is contoured as a groove which is dimensioned to receive the patellar ridge in a complementary manner. Proper dynamic function of the patello-femoral joint requires that the patellar ridge accurately track the underlying trochlear groove when the knee is moved through flexion or extension. The anatomy and function of the patello-femoral joint are well known and described in detail in Ficat, R. P. et al., Disorders of the Patello-femoral Joint, Williams & Wilkins, 1977.
Functional disorders of the patello-femoral joint frequently relate to improper dynamics. Less severe forms of patello-femoral joint disorder cause pain in the joint, but do not exhibit errors in patellar tracking of the trochlear groove. In more severe forms of patello-femoral joint disorder, patellar tracking errors are evident in addition to joint pain, but there is no subluxation or dislocation of the joint. In still more severe forms of patello-femoral joint disorder, patellar tracking errors result in subluxation or dislocation of the joint. Recurrent subluxation of the patello-femoral joint is a particular disorder whereby the patella deviates transiently and typically rapidly from its normal axis of movement due to patellar tracking errors during movement of the knee. Slight deviations of the patella from its normal axis of movement are termed minor subluxation and may not produce any clinically apparent relocation of the patella. Minor subluxation is often the result of a functional imbalance in the knee. Significant deviations of patellar movement which approach dislocation are termed major subluxation. Major subluxation can be brought on by strenuous activity although it often occurs even in the absence of such activity. Recurrent patellar subluxation, both major and minor, is a relatively frequent condition among women generally and particularly among women athletes.
Most instances of subluxation or dislocation of the patella due to patellar-tracking errors are in the lateral direction because biomechanical forces typically bias the patella laterally when the knee is load-bearing. In addition, subluxation or dislocation of the patella due to patellar tracking errors has the greatest risk of occurring when the knee is approaching extension. When the knee ranges between about 30° of full extension and full extension, the trochlear groove becomes relatively small and shallow which is conducive to subluxation or dislocation. Functional disorders of the patello-femoral joint are highly undesirable because such disorders may ultimately lead to cartilage damage and arthritis of the knee. Therefore, a recognized need exists for effective preventative or remedial treatment of patello-femoral joint disorders.
It is an object of the present invention to provide a knee orthosis which prevents or remediates functional disorders of the patello-femoral joint including recurrent patellar subluxation or dislocation. More particularly, it is an object of the present invention to provide a knee orthosis which reduces the risk of patellar tracking errors by providing the knee with a patellar tracking guide. It is a specific object of the present invention to provide a knee orthosis which applies a patellar tracking guide to the head of the femur laterally or medially adjacent to the patella to reduce the risk of recurrent lateral or medial patellar subluxation or dislocation. It is a further object of the present invention to provide a knee orthosis having a patellar tracking guide which dynamically tensions when the knee approaches the extension position for maximum effect and dynamically relaxes when the knee approaches the flexion position to minimize interference with the function of the knee. It is still a further object of the present invention to provide a knee orthosis having a patellar tracking guide which is dynamically positioned more proximal to the patella when the knee approaches the extension position for maximum effect and is dynamically positioned more distal to the patella when the knee approaches the flexion position to minimize interference with the function of the knee. These objects and others are accomplished in accordance with the invention described hereafter.